Mendel's principle of dominance suggests a (recessive, diploid, dominant) gene will always be masked by the presence of a (recessive, haploid, dominant) gene.

The correct answer for the blanks are-

1) Recessive gene

2) Dominant gene

Explanation:

According to Mendel's principle of dominance, offsprings with heterozygous genotype (that is having two different alleles, dominant and recessive) exhibit the phenotype of dominant allele as it masks the expression of recessive allele.

Thus, a recessive allele (such as t for dwarf plant) will always be masked by the presence of dominant allele (such as T for tall plant).

Therefore, a Tt (heterozygous pea plant) genotype plant will express tall trait and mask dwarf trait.

Thus, according to this law, the right answer for blanks are-

1) Recessive gene

2) Dominant gene.